This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Appln. No. 199 50 109,2 filed in Germany on Oct. 18, 1999; the entire content of which is hereby incorporated by reference
The present invention relates to a rotor for a gas turbine, and more particularly to cooling rotor blades.
An example of a rotor having a cooling arrangement is disclosed in U.S. Pat. No. 4,505,640 and is illustrated in FIG. 1. The rotor 10 comprises a rotor disk 11 at whose periphery are arranged a multiplicity of location slots 13 essentially extending in the axial direction and separated from one another by rotor teeth 12. Cooling air supply passages 14, which extend in the rotor disk 11 and provide cooling air for cooling the rotor blades 16, emerge from below into the location slots 13. The rotor blades 16, which each have a blade airfoil 17, a blade root 19 and a platform 18 which is arranged above the blade root 19, are pushedxe2x80x94together with the blade root 19xe2x80x94in the axial direction into the location slot 13 and are there releasably retained, a positive connection being usually achieved by means of a fir-tree configuration of the cross-sectional profile. Hollow spaces 21 are formed between the platforms 18 and the peripheral surface 15, which is located underneath, of the rotor disk 11. The cooling air (or another suitable cooling medium) introduced by means of the cooling air supply passage 14 is fed through ducts (not shown) within the blade root 19 to the inside of the (hollow) blade airfoil 17, where it flows and is then allowed to escape through outlet openings on the blade airfoil 17 and/or on the platform 18.
In the rotor blade 16, it is necessary (for reasons of thermal load-carrying capability) for the cooling medium to cool not only the actual blade airfoil, by means of the cooling medium flowing within it, but also to cool the blade root 19 and the platform 18 arranged above the blade root.
In the past, a multiplicity of proposals have been made for cooling these partial regions of the rotor blade.
In U.S. Pat. Nos. 4,012,167, 5,639,216 and 5,848,876, for example, it is proposed that horizontally extending cooling air ducts should be accommodated within the platform, these being supplied with cooling air in various ways. Such internal cooling of the platform is, however, very complicated from the point of view of manufacturing technology because it is difficult to create appropriate ducts in, for example, cast blades.
U.S. Pat. No. 5,800,124, furthermore, proposes the configuration of cover plates laterally arranged in the root region in such a way that cooling air is blown from below onto the rear edge of the blade platform through corresponding vertical ducts in the cover plates. Cooling of the complete platform is not possible by this means.
U.S. Pat. No. 5,738,489 proposes attaching, to the bottom of the platforms, a thermal conductor which removes the heat from the platform and conveys it to the central cooling air duct in the blade root. Such a solution is likewise complicated from a manufacturing technology point of view because, in this case, special materials must be additionally attached to the blade. Furthermore, it is not possible to flush the hollow spaces below the platform with cooling air in this way.
Finally, U.S. Pat. No. 5,340,278 proposes the provision of holes extending obliquely downward at the level of the platform, cooling air from the central cooling air duct of the blade being blown through these holes into the hollow spaces below the platform. Although this does permit the platform to be cooled and the hollow spaces to be flushed, the holes are likewise very complicated to manufacture.
In rotor blades which are fed with cooling air from the rotor end, furthermore, it is usual to employ the cooling air which flows past the fastening for cooling the platform or at least for flushing the hollow spaces. The quantity of cooling air is indeterminate because it depends on the fit between the blade root and the location slot and is more equivalent to a leakage.
The object of the invention is, therefore, to create a rotor in which, in a simple manner from the point of view of manufacturing technology, cooling medium or cooling air can be brought in a defined quantity from the rotor-end cooling air supply passage into the hollow spaces below the platform.
The invention achieves this object by forming cooling air ducts between the outside of the blade root and the inside of the location slot, which cooling air ducts can be simply manufactured, for example as recesses, and guide the cooling medium on a direct path from the cooling air supply passage into the hollow spaces.
A preferred embodiment of the rotor in accordance with the invention is characterized in that the cooling air ducts are at least partially configured as recesses in the blade root and/or location slot. These recesses can be formed directly, in a particularly simple manner, during casting or they can be manufactured by subsequent material removal.
This is particularly simple if, in accordance with a preferred development of this embodiment, the cooling air ducts are configured as recesses which extend vertically between the outlet of the cooling air supply passage and the hollow spaces.
Another preferred development is characterized in that the cooling air ducts are configured as recesses which, on the one hand, extend horizontally outward from the outlet of the cooling air supply passage to an end surface of the blade root end, on the other hand, extend vertically upward on the end surface and into the hollow spaces, and in that the end-surface recesses are sealed toward the outside by cover plates, in that axial locking plates, which are arranged at the end surface, are provided to secure the rotor blades axially in the location slots, and in that the axial locking plates are employed as cover plates.
A further preferred development is distinguished by the fact that a cooling air duct is configured as a recess which leads horizontally outward from the outlet of the cooling air supply passage to an end surface of the blade root, in that an axial locking plate, which is arranged at the end surface, is provided to secure the rotor blade axially in the location slot, and in that the axial locking plate is shaped in such a way that a cooling air duct is formed which extends vertically upward between the axial locking plate and the end surface of the blade root and into the hollow spaces. The formation of the cooling air ducts can, in this way, be effected at least partially by a comparatively simple shaping of the axial locking plates.